Power circuit-breakers are employed in electricity distribution networks for the protection of down-circuit installations against damage associated with an overload or short-circuit. To this end, power circuit-breakers incorporate electromagnetic, thermal or electronic tripping means which, upon the overshoot of a predetermined current value, e.g. in the event of an overload or a short-circuit, trigger an actuating mechanism which, in turn, executes the opening of the power circuit-breaker. A power circuit-breaker thus tripped interrupts the supply of electricity to down-circuit components in the electricity network, thereby protecting the latter against damage associated with high overload and/or short-circuit currents.
In many cases, in widely-ramified electricity distribution networks, a plurality of series-connected power circuit-breakers are selectively employed in a staggered manner. By this, it is understood that, in the event of a fault, for example a short-circuit, only the load-adjacent power circuit-breaker which is closest to a load is tripped in the first instance, whereas a load-distant power circuit-breaker, which is superordinate in the electricity distribution network hierarchy to the load-adjacent power circuit-breaker, is not tripped. In other words, in the event of a fault, only the power circuit-breaker which is closest to the incident interrupts the flow of current. In this manner, the supply of current to other parts of the electricity distribution network, which are not directly affected by the fault, can be maintained. Power circuit-breakers which operate in this selective manner are also described as selective power circuit-breakers. Selectivity is achieved, in that the load-distant power circuit-breaker is tripped with a time delay in relation to the load-adjacent power circuit-breaker. Such a time delay can be set, for example, electronically or mechanically.
Delayed opening of this type can be problematic in the case of very high short-circuit currents on the grounds that, as a result of the predetermined time delay, the selective power circuit-breaker will not trip until the magnitude of the short-circuit current has already resulted in the direct damage, or even the destruction of the power circuit-breaker itself. In the event of very high currents, the electromagnetic effects of the currents flowing in the switching contacts are so great that the switching contacts of the power circuit-breaker, as a result of electromagnetic repulsion, are subject to short-term mutual disengagement. This results in the generation of an arc between the opened switching contacts. Such arcs have a high destructive force, and can cause permanent damage to a power circuit-breaker and the reduction of its service life. Given that, in a selective power circuit-breaker, direct opening is not desired in the first instance, the switching contacts reclose after a short-term disengagement of the contacts. Further arcing is generated as a result. In this case, the self-protection function of the power circuit-breaker is thus eliminated, as a result of the predetermined time delay.
In order to circumvent the predetermined time delay in selective power circuit-breakers in the event of very high short-circuit currents, various measures have already been implemented.
DE 202 14 922 U1 thus discloses a power circuit-breaker with instantaneous short-circuit trip devices, wherein the instantaneous short-circuit trip devices comprise hinged armatures which, in the event of high short-circuit currents due to electromagnetic effects, execute a rotating motion against the force of a spring element, as a result of which the actuating mechanism of the power circuit-breaker is tripped and the switching contacts of the power circuit-breaker are fully opened. By means of the specific configuration of the spring element, the response behaviour of the instantaneous short-circuit trip devices can thus be influenced such that the hinged armatures only break away upon the overshoot of a short-circuit current of a predetermined magnitude. As a result of the special geometry of the hinged armatures, the instantaneous short-circuit trip devices only respond beyond the trip threshold of the normal short-circuit tripping means which are present on the power circuit-breaker, but significantly more rapidly than the latter.
Moreover, the exploitation of the pressure increase associated with the generation of an arc in selective power circuit-breakers is also already known. In the interests of the most rapid quenching possible, arcs in a power circuit-breaker are conducted by appropriate means to an arc chute, and are quenched therein. As a result of the high energy of the arc, this is associated with an extremely rapid pressure increase in the arc chute. This pressure increase can be exploited with respect to the selectivity and the simultaneous self-protection of power circuit-breakers.
Thus, for example, DE 691 10 540 T2 describes a selective power circuit-breaker with a pressure trip unit. To this end, the trip unit of the power circuit-breaker, in addition to an overload and/or short-circuit capture element which, in the event of a fault, delivers a signal to a switching mechanism for the automatic opening of the power circuit-breaker, comprises an actuating element which responds to a pressure increase in a separation zone of the switching contacts associated with the generation of an arc, and actuates the opening mechanism. The actuating element comprises a moving component, for example a piston, which is exposed, firstly to the overpressure generated in the arc chute, via a connection line which is arranged between the pressure trip unit and the arc chute, and secondly to an appropriate effective force delivered by a return device, for example a return spring. A displacement of the piston against the force of the return spring thus initiates the tripping of the opening mechanism of the power circuit-breaker, wherein the return device is adjusted such that any spurious tripping in response to a simple overload is prevented.
In other words, the power circuit-breaker described in DE 691 10 540 T2, additionally to the trip mechanism which is customarily provided, incorporates an actuating element which responds to an overpressure in the arc chute, wherein a pressure threshold can be set by means of a return device such that the actuating element, upon the occurrence of an arc with a very high current, responds very rapidly and actuates a rapid tripping of the power circuit-breaker whereas, for the disconnection of a normal or small current, it shows practically no response, as the overpressure generated in the arc chute is not sufficient to overcome the force of the return device. In this manner, a circuit-breaker is provided which can be employed selectively, but which simultaneously incorporates a self-protection function in the event of very high currents.
The above-mentioned power circuit-breaker has a disadvantage in that, in a three-pole power circuit-breaker, the three poles are respectively connected by means of ducts to a collection chamber, which in turn incorporates a connection to the pressure chamber of the overpressure actuating element. The individual ducts, in the region of their entry to the collection chamber, are provided with non-return values, in order to prevent any flow of gas from one pole to another. Accordingly, the overpressure generated in one pole must firstly be propagated through the duct system before it can act on the actuating element in the pressure chamber. As the overpressure actuating element is arranged at some distance from the arc chute, this can result in both a pressure loss and a time delay within the duct system, with a respective negative impact upon the response behaviour of the actuating element. The system is moreover comprised of a plurality of individual components, thereby resulting in a pressure tripping system of complex design, which is susceptible to wear.
From U.S. Pat. Nos. 8,947,182 B2, 3,631,369, US 2015/0200066 A1 and WO 01/69630 respectively, selective trip devices are also known, having overpressure-responsive actuating elements. In this case, however, the respective actuating element is arranged in a flow duct of the circuit-breaker which functions as an exhaust duct. Via this exhaust duct, gas which is generated in conjunction with the ignition of an arc is discharged from the arc chute. In order to fulfil this function, the exhaust duct must remain open, and the forces acting on the actuating element arranged in the exhaust duct must be generated exclusively by the prevailing flux in the exhaust duct, which is perceived as disadvantageous. Moreover, an open system of this type is highly susceptible to fouling, as the pressure trip unit is directly exposed to the gases leaving the arc chute.